Carbon dioxide ice clouds, snowfalls, and baroclinic waves in the northern winter polar atmosphere of Mars

The formation of CO₂ ice clouds in the northern winter polar atmosphere of Mars and their relation to baroclinic planetary waves, which dominate local dynamics, are studied using a general circulation model. The simulation shows that clouds are formed at altitudes of up to ∼ 40 km, and their occurrence correlates to a large degree with the cold phases of transient planetary waves. Ice particles formed up to ∼ 20 km can reach the surface in the form of snowfall in certain longitude regions, while in others, these particles likely sublimate in the lower warmer atmospheric layers. The simulation suggests that about a half of the seasonal ice cap is created by CO₂ snow, while the remaining half by direct condensation on the surface. Thus, the occurrences of ice clouds and rates of deposition are closely linked to traveling planetary waves, indicating the possibility for the reliable forecasts of CO₂ snow storms. Key Points CO₂ ice clouds in polar winter are closely aligned with planetary waves CO₂ ice cap is mostly formed by snowfalls from below 20 km Close connection of clouds and waves can form a basis for snow storm forecasts.